The present disclosure relates to a method for monitoring, an apparatus for monitoring and a monitoring apparatus for monitoring.
Digital sensors and sensors with analog clocking often require a clock for operation. This clock can either be supplied externally or can be generated by means of an oscillator. In the case of rotation rate sensors, the mechanical sensor itself is used as an oscillator in order to generate an internal clock using an ordinary phase locked loop circuit (PLL). For sensors with safety-critical functions, which are used in the sensor system of vehicle stabilization programs (ESP), for example, a great demand is made on the dependability of the sensor. This includes monitoring the clock used, inter alia. Firstly, the monitoring is used to draw conclusions about the internal signal processing, and secondly, in the case of rotation rate sensors, conclusions can be drawn about the mechanical functionality of the sensor element if the frequency which can be derived from the clock used is monitored.
Today, four types of frequency monitoring operations are known and to some extent are used in current Bosch sensor generation, such as MM3 or MM5, or possibly even in competing products. The following methods are used:    1) Logic monitoring, using a digital interface, for example SPI.    2) Monitoring by means of a second, externally supplied clock.    3) Monitoring using a crystal or other type of oscillator, which is used in addition to the mechanical oscillator.    4) Monitoring by means of a clock which is provided externally by the sensor and is monitored by an external unit.
DE 103 47 413 A1 shows a controller with clocked data transmission between a processor and at least one further circuit, wherein the processor itself outputs the clock. The processor monitors the clock using the output signals from at least two clock outputs.